(a) Field of the Invention
The present invention relates to a vehicle driving system and method, and more particularly to a system and method for driving a motor after pre-charging a capacitor included in an inverter of an electric vehicle.
(b) Description of the Related Art
An electric vehicle has been actively studied since it is a highly possible alternative capable of solving vehicle problems on pollution and energy in future.
The electric vehicle (EV) is a vehicle that mainly gets power from a battery to drive an alternating current (AC) or direct current (DC) motor, which is broadly classified into a battery-only electric vehicle and a hybrid electric vehicle. The battery-only electric vehicle employs power from a battery to drive the motor and has to be recharged when the power is used up. On the other hand, the hybrid electric vehicle runs an engine to generate electricity and charge the battery and uses this electricity from the battery to drive the motor.
Further, the hybrid electric vehicle is classified into a series type and a parallel type. In the series hybrid electric vehicle, mechanical energy from the engine is transformed into electric energy trough a generator, and the electric energy is supplied to the battery or the motor so that the vehicle can be always driven by the motor. In other words, the series hybrid electric vehicle is achieved by adding the engine and the generator to the existing electric vehicle in order to increase mileage. On the other hand, the parallel hybrid electric vehicle can be driven by only the motor using the battery power, or only the engine using gasoline or diesel, or both the engine and the motor in accordance with driving conditions.
With recent development of the motor/control technology, there has been developed a high-power, small and high-efficient system. As the DC motor is replaced by the AC motor, the electric vehicle has been greatly improved in output and performance (e.g., accelerating ability and the maximum speed) and thus reached a level comparing favorably with a gasoline vehicle. The high power causes high speed, and thus the motor becomes light and small, thereby decreasing the loading weight or volume of the motor.
In addition, a mild hybrid system has been on the rise. In the mild hybrid system, the electric vehicle employs not a high-voltage battery (e.g., about 270V) but a low-voltage battery (e.g., 48V).
An electric vehicle with this mild hybrid system includes a plurality of relays as a switching means in a battery system, in order to supply or break a current charged in the battery. Further, the battery system of the electric vehicle with the mild hybrid system includes a pre-charge circuit for previously charging a capacitor of an inverter in order to prevent the capacitor from explosion or the like.
Major issues in the low-voltage battery system for the mild hybrid system are how to make the battery system inexpensive, small and lightweight. However, it is difficult to make the battery system inexpensive, small and lightweight since the pre-charge circuit is involved in the battery system.
Accordingly, it is requested to remove the pre-charge circuit from the battery system.